Apparatus for sealing flex circuits having heat sensitive circuit elements

ABSTRACT

A method and apparatus is disclosed for affixing a cover layer formed of liquid crystal polymer to a flex circuit consisting of circuit elements mounted to a liquid crystal polymer substrate in order to encapsulate the circuit elements between the cover layer and substrate to protect them from exposure to moisture and contaminants and to provide thermal protection of temperature sensitive circuit elements within the flex circuit during the encapsulation process.

This application is a divisional of U.S. application Ser. No.11/050,303,filed on Feb. 3, 2005 now U.S. Pat. Ser. No. 7,128,801.

FIELD OF THE INVENTION

This invention is directed to flexible circuits, and, more particularly,to a method and apparatus for sealing circuit elements of a flexiblecircuit, including heat sensitive circuit elements, which are mounted ona substrate formed of liquid crystal polymer to protect them fromexposure to moisture and contaminants.

BACKGROUND OF THE INVENTION

Flexible or “flex” circuits are used in a wide variety of applicationswhere an electrical circuit must bend around corners or be flexed duringoperation. Flex circuits are thin, light weight, flexible and exhibithigh routability. Traditionally, polyimide films have been used assubstrates in the manufacture of flex circuits due to their good thermalstability and mechanical strength. Other properties of polyimide films,however, limit the speed or frequency at which electric componentsmounted thereto can operate.

Liquid crystal polymer (“LCP”) has been developed in recent years as areplacement for polyimide films in flex circuits. LCP is a thermoplasticaromatic polyester which is thermally stable, with an upper usetemperature in excess of 250° C. and good inherent flame retardantproperties. LCP films, in comparison to polyimide films, have aboutone-tenth of the moisture uptake and a lower coefficient of humidityexpansion. Lower moisture absorption leads to higher frequency signaland data processing stability. Additionally, LCP films have a lowerdielectric constant and a lower loss or dissipation factor over thefunctional frequency range of 1 kHz to 45 GHz, with negligible moistureeffects, compared to polyimide films.

The fabrication of flex circuits with LCP films is expected to lead totheir use in more demanding environments where moisture and othercontaminants are prevalent. Particularly in such types of applications,the circuit elements applied to the LCP substrate of the flex circuitmust be protected from damage. Soldermask coatings, which have beenemployed to provide protection from moisture and contaminants inpolyimide films, have been considered for use with LCP substrates.Additionally, due to the thermoplastic nature of LCP, the application ofan LCP film cover layer to an LCP substrate has been proposed as a meansof encapsulating circuit elements. With respect to LCP cover layers,current practice is to employ an air knife or laser to create localizedheating of the LCP cover layer and LCP substrate along the periphery ofthe flex circuit. A number of problems can arise from this approach. Afailure of the seal between the cover layer and substrate at any pointalong the periphery of the flex circuit can expose all of the circuitelements to moisture, chemicals or other contaminants. If the airbetween the cover layer and substrate is not fully removed,pressurization of the flex circuit which would occur in underwaterapplications, for example, could compress such air and create a bubblepotentially resulting in a rupture of the cover layer and/or substratethus creating a failure of the entire circuit.

The melt temperature of LCP material is approximately 283° C., andsoldermask coatings are also applied at relatively high temperatures.While a number of standard circuit elements are not affected by hightemperatures, components such as micro-electrical-mechanical-system(“MEMS”) sensors, infra-red sensors and a variety of other circuitelements are temperature sensitive and can be damaged or destroyed uponexposure to elevated temperatures. There is a need for an efficient anddependable method and apparatus capable of individually sealing orencapsulating the electrical components of circuits which employ an LCPsubstrate, while protecting heat sensitive components of the circuitfrom damage due to the temperatures at which the sealing process isperformed.

SUMMARY OF THE INVENTION

This invention is directed to a method and apparatus for affixing an LCPcover layer to a flex circuit consisting of circuit elements mounted toan LCP substrate, at least some of which are temperature sensitive, inorder to individually protect the circuit elements from damage and/orreduced operational efficiency due to the presence of moisture, chemicaland other contaminants.

In the presently preferred embodiment, the apparatus includes aniso-static press having a hollow interior connected to a source of oilor other liquid whose temperature can be accurately controlled andmaintained. The oil is heated to a temperature in the range ofapproximately 283° C. to 320° C. and transferred from a reservoir intothe interior of the press. The base of the press has a plate or membraneformed of a flexible material covered with a non-stick surface whichdoes not adhere to LCP.

The flex circuit is placed on the surface of the thermally conductivetop plate of a support such that the circuit elements are exposed. Athermal insulating compound may be placed over each temperaturesensitive circuit element for added thermal protection. The supportincludes a housing formed with a cavity within which a number ofconduits are mounted each having an upper end communicating with achannel formed in the underside of the top plate. Cooling fluid from asource is circulated through selected conduits, i.e. those which arelocated beneath the temperature sensitive circuit elements of the flexcircuit, to provide localized cooling of such elements during thelamination process. Other conduits, which are not located near thetemperature sensitive circuit elements, may be supplied with a heatingfluid to raise the temperature of the top plate of the support inselected areas and thus assist with the lamination process.

With the flex circuit in place on the top plate of the support, and theconduits within the support receiving cooling fluid or heating fluid tocool or heat selected areas of the top plate, an LCP cover layer isplaced atop the flex circuit and the press is activated to move intocontact with the cover layer. The flexible membrane at the base of thepress is capable of substantially conforming to the shape of the circuitelements, thus urging the LCP cover layer around each of themindividually to the underlying LCP substrate of the flex circuit. Thetemperature and pressure applied by the press, and the elevatedtemperature of selected areas of the support top plate, are sufficientto cause the LCP cover layer and substrate to “relax” or melt to alimited extent and thus adhere together forming a secure bond so thatthe circuit elements are individually encapsulated between the twolayers.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure, operation and advantages of the presently preferredembodiment of this invention will become further apparent uponconsideration of the following description, taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a schematic, perspective view of the apparatus of thisinvention;

FIG. 2 is a block diagram illustrating the operation of the press of theapparatus shown in FIG. 1;

FIG. 3 is a perspective view of the support for the flex circuit with aportion cut away to show the conduits mounted within a cavity in thesupport;

FIG. 4 is a schematic view of one conduit of the support connected by3-way valves to a hot fluid source and a cold fluid source, whereincooling fluid is being supplied to the conduit;

FIG. 1A is an enlarged view of the encircled portion of FIG. 1;

FIG. 5 is a view similar to FIG. 4, except with hot fluid being suppliedto the conduit;

FIG. 6 is a schematic, block diagram depicting the structure forsupplying hot fluid and cooling fluid to the conduit; and

FIG. 7 is a cross sectional view of the connection between a conduit andthe top plate of the support.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the Figs., the apparatus 10 of this invention isschematically illustrated. The apparatus 10 includes an iso-static press12 having a housing 14 formed with a hollow interior. The base of thehousing 14 mounts a flexible membrane 16 having an exposed surfacecoated with Teflon® or other release agent which will not stick to LCP,and an inside surface coated with a hydrophobic film. Preferably, theflexible membrane 16 is formed of high density polyethylene, butylrubber, ethylene propylene diene monomer rubber or a similar material.

The press 12 is operative to apply heat and pressure against a coverlayer 18 which overlies a flex circuit 20 placed upon a support 22. Inthe presently preferred embodiment, the press 12 is heated by theintroduction into its hollow interior of heated oil or a similar fluidwhose temperature can be relatively accurately controlled and maintainedwithin the range of about 283° C. to 320° C. A first reservoir 24 havingheating elements (not shown) is connected by a supply line 26 to amanifold 28. A pump 30 and valve 32 are located in the supply line 26,between the first reservoir 24 and manifold 28, as shown. The manifold28, in turn, is connected by an input line 34 to one port at the top ofthe press 12, and by an output line 38 to a second port. A recirculationline 42, containing a valve 32, is connected between the manifold 28 andthe top of the first reservoir 24.

In view of the relatively high temperature obtained by the press 12during operation, it is advantageous to provide a cooling capability tostep the temperature down. To that end, a second reservoir 44 isprovided which contains the same fluid as first reservoir 24 except atambient temperature. The bottom of second reservoir 44 is connected by aline 46 to the manifold 28, and a recirculation line 48 connects themanifold 28 to the top of the second reservoir 44. A pump 30 and valve32 are located in the line 46 between the second reservoir 44 andmanifold 28, and a valve 32 is mounted in the recirculation line 48.

The press 12 is moved with respect to the support 22 by a number ofpneumatic or hydraulic pistons 50 which are mounted at equal intervalsalong the top surface of the press 12. Conventionally, the pistons 50are independently actuated by a source of air or fluid (not shown) toensure that the press 12 applies uniform pressure to the cover layer 18and flex circuit 20 over the entire surface area of the flexiblemembrane 16. The detailed construction of the press 12 forms no part ofthis invention, and is therefore not discussed further herein.

As discussed above, the method and apparatus 10 of this invention aredesigned to provide a means for individually encapsulating circuitelements to protect them from moisture and contaminants. The flexcircuit 20 consists of a substrate 52 formed of LCP—upon which a numberof circuit elements 54 are mounted. The cover layer 18 is also formed ofLCP, which, because of its thermoplastic nature, will “relax” or beginto melt at a temperature of about 283° C. By placing the cover layer 18over the flex circuit 20 and applying heat and pressure, the cover layer18 and substrate 52 adhere to one another with a secure bond andentirely enclose the circuit elements 54 between them.

At least some of the circuit elements 54 are temperature sensitive andwould be damaged by exposure to heat on the order of the melttemperature of the LCP layers. The support 22 is constructed to providelocalized cooling of the temperature sensitive circuit elements 54, andto generate heat in other areas of the substrate 52 which raises itstemperature to assist with the lamination or encapsulation process. Withreference now to FIGS. 3-7, the support 22 includes a side wall 56defining an internal cavity 58 which is closed by a top plate 60 and abottom plate 62. The top plate 60 is preferably formed of a highlythermally conductive material such as aluminum silica carbide. A numberof channels 64 are machined or otherwise formed in the underside of thetop plate 60, each of which mounts a conduit 66. See FIG. 7. Theconduits 66 are depicted in the Figs. as a pair of side-by-side pipes 68and 70 each having an upper end received within a channel 64 in the topplate 60 so that fluid can pass between the two. It should beunderstood, however, that the conduit 66 may be a unitary structureformed with an internal wall so as to define two separate flow paths,for purposes to become apparent below.

An array of conduits 66 is carried within the cavity 58 of the support22 atop the bottom plate 62 and extending beneath substantially theentire surface area of the top plate 60. Structure is provided totransmit either cold fluid or hot fluid into each conduit 66, dependingon the position of the temperature sensitive circuit elements 54 restingon the top plate 60 of the support 22, so that such fluid produceslocalized heating or cooling of the top plate 60. As best seen in FIGS.4-6, this structure includes a cold fluid source 72 connected to a pump74, which, in turn, is connected to a distribution manifold 76 and, ahot fluid source 78 connected by a pump 80 to a second distributionmanifold 82. While the “hot” fluid source 78 is shown as a separatereservoir in the Figs., it is contemplated that the first reservoir 24supplying heated fluid to the press 12 may be employed to transmit hotfluid to the conduits 66, if desired.

As described more fully below in connection with a discussion of theoperation of the apparatus 10 of this invention, the distributionmanifold 76 connected to the cold fluid source 72 transmits such fluidto number of 3-way valves 84. Each 3-way valve 84, in turn, is connectedto the inlet of the pipe 70 of a conduit 66. Similarly, the distributionmanifold 82 receiving hot fluid from source 78 is connected to a numberof 3-way valves 86, each of which connects to the inlet of a pipe 68 ofa conduit 66. Consequently, depending upon the operative position of the3-way valves 84 and 86, either hot or cold fluid can be circulatedthrough each conduit 66 to obtain localized heating or cooling of thetop plate 60 in the area located immediately above such conduit 66.

The operation of the press 12 of this invention is described initiallybelow, followed by a discussion of the localized cooling and heatingprovided by the support 22.

The apparatus 10 is operated by a commercially available controller 56as schematically depicted in the block diagrams of FIGS. 2 and 6.Initially, oil or other fluid within the first reservoir 24 is broughtup to a temperature in the range of 283° C. to 320° C. by activatingheating elements (not shown) therein. The controller 56 is operative toactivate the heating elements via a signal input through lead 88, orthey may be independently activated by a switch (not shown) located atthe first reservoir 24. The controller 56 then inputs signals throughleads 90 and 92 to start the pump 30 and open valve 32, respectively,thus initiating the flow of heated oil out of the first reservoir 24.When it is desired to heat the press 12 in preparation for circuitencapsulation, the controller 56 deactivates the pump 30 and valve 32 inline 46 from second reservoir 44 by signals input through leads 94 and96, respectively. The heated oil flows to the press 12 through themanifold 28 and into the input line 34 leading into the interior of thepress 12. Preferably, the temperature of the heated oil within the press12 is controlled and maintained by continuously recirculating it fromthe first reservoir 24 through the manifold 28 and input line 34 intothe press 12, and then out of the press 12 through the output line 38and manifold 28 to the recirculation line 42 connecting the manifold 28to the first reservoir 24. The controller 56 opens the valve 32 withinthe recirculation line 42 via a signal through the line 98 to allowheated oil to pass from the manifold 28 into the first reservoir 24.

With the press 12 at the appropriate temperature, the encapsulationprocess can proceed. The flex circuit 16 is positioned on the support 22so that the circuit elements 54 on the LCP substrate 52 are exposed. Inthe presently preferred embodiment, a thermal insulating compound 99such as Aerogel or a silica based material is placed over the top ofeach temperature sensitive circuit element 54. See FIG. 1A. The compound99 is effective to assist in preventing thermal damage to the upperportion of such circuit elements during the encapsulation operation. TheLCP cover layer 18 is then placed atop the substrate 52 and circuitelements 54. The controller 56 operates the pistons 50 causing the press12 to move toward the support 22. Upon engagement of the flexiblemembrane 16 at the bottom of the press 12 with the cover layer 18, at auniform pressure up to 200 psi, the flexible plate 16 substantiallyconforms to the shape of the circuit elements 54 beneath. In turn, thecover layer 18 is forced around the circuit elements 54 into contactwith substrate 52. The press 12 is maintained in this position for aperiod of time sufficient to heat both the LCP cover layer 18 and LCPsubstrate 52 to a melt temperature of at least 283° C., but not morethan about 320° C., causing them to bond to one another and thusencapsulate the circuit elements 54 between the two.

After completing one or more encapsulation procedures, the temperatureof the press 12 may be stepped down by circulating comparatively cool,ambient temperature oil into the press 12 from the second reservoir 44.The controller 56 is operative to deactivate the pump 30 and close valve32 within line 26 connected to the first reservoir 24, while activatingpump 30 and opening valve 32 within the line 46 connected to the secondreservoir 44. The controller 56 closes the valve 32 within therecirculation line 42, and then opens the valve 32 within therecirculation line 48 extending from the manifold 28 to the secondreservoir 44 by inputting a signal to such valve 32 through a line 100.As a result, ambient temperature oil is recirculated within the press 12to reduce its temperature.

As noted above, a thermal insulating compound 99 is placed on the topsurface of the temperature sensitive circuit elements 54 prior to theencapsulation operation to aid in the protection of them from the heatof the press 12. For additional thermal protection, it is desirable toprovide localized cooling of the top plate 60 of support 22 in thoseareas located immediately beneath the circuit elements 54. Additionally,the encapsulation process may be enhanced by heating areas of the topplate 60 which are spaced from the thermally sensitive circuit elements54. The support 22 provides such localized heating and cooling asfollows.

For purposes of the present discussion, and with reference initially toFIGS. 4 and 6, a single conduit 66 including pipes 68 and 70 is shown.It should be understood that the following discussion describing themanner in which cold fluid or hot fluid is supplied to conduit 66applies equally to all of the other conduits 66 mounted within thesupport 22. One of the 3-way valves 84 is connected to the inlet of pipe70 of conduit 66 by a line 102, and one of the 3-way valves 86 isconnected to the inlet of pipe 68 of conduit 66 by a line 104. The 3-wayvalve 84 is also connected to the hot fluid source 78 through a line106, and the 3-way valve 86 is connected to the cold fluid source 72 bya line 108. In order to circulate cold fluid through the conduit 66, andinto contact with the underside of the top plate 60 immediately abovethe conduit 66, the controller 56 inputs a signal through line 110 toactivate the pump 74 so that it begins pumping cold fluid from thesource 72 into the distribution manifold 76. The operation of pump 80 isgoverned by the controller 56 via signals input through line 112, asdescribed below in connection with a discussion of FIG. 5. The coldfluid passes from the pump 74 into the distribution manifold 76 and thento the inlet of each of the 3-way valves 84. It should be understoodthat the three valves 84 and three valves 86 shown in FIG. 6 are forpurposes of illustration, and there could be essentially any number ofvalves 84, 86 depending on how many conduits 66 are employed in thesupport 22.

As best seen in FIG. 4, flow of cold fluid or heated fluid into eachindividual conduit 66 is dependent on the operation of a valve pair,i.e. one of the 3-way valves 84 and one of the 3-way valves 86. Once theposition of the thermally sensitive circuit elements 54 on the top plate60 of support 22 is determined, the group(s) of conduits 66, orindividual conduits 66, which are located immediately beneath such areasare identified. The controller 56 is operative to introduce cold fluidinto such conduit(s) 66 as follows. A signal is input to 3-way valve 84though a line 114 which opens a path through 3-way valve 84 to the line102 connected to the inlet of pipe 70, but closes the flow path to line106 which connects such valve 84 to the hot fluid source 78. At the sametime, the controller 56 inputs a signal through line 116 to the 3-wayvalve 86 connected to the pipe 68 associated with that conduit 66. The3-way valve 86 is operated to permit the flow of fluid from pipe 68 intothe line 108 connecting 3-way valve 86 to the cold fluid source 72,while closing the flow path through 3-way valve 86 from the distributionmanifold 82. Consequently, cold fluid from the source 72 is pumped viapump 74 through the distribution manifold 76, to the 3-way valve 84, andthen into the pipe 70 of conduit 66 via line 102. The cold fluid isdirected by pipe 70 into the channel 64 formed on the underside of thetop plate 60 where it contacts and reduces the temperature of a discretearea of the top plate 60 beneath one or more temperature sensitivecircuit elements 54. See also FIG. 7. The cooling fluid passes throughthe channel 64 and enters the pipe 68 of conduit 66 from which it isdischarged into the line 104 leading to the 3-way valve 86. The 3-wayvalve 86 passes the cold fluid into line 108 where it is transmittedback to the cold fluid source 72. The cold fluid is continuouslyrecirculated along the above-described flow path, as depicted by arrows118 in FIG. 4, throughout the encapsulation process to assist inprotection of the temperature sensitive circuit elements 54 from thermaldamage.

Other areas of the flex circuit 20 mount circuit elements 54 which arenot affected by the temperature of the encapsulation process. In theseareas, it is desirable to locally heat the top plate 60 of the support22 to assist the press 12 with the encapsulation process. The same valvearrangement described in FIG. 4 is employed to deliver hot fluid to eachindividual conduit 66. With reference to FIGS. 5 and 6, in order toobtain a flow of hot fluid into the conduit 66 the controller 56 inputsa signal though line 112 to start the pump 80 connected to the hot fluidsource 78. The hot fluid passes through the distribution manifold 82 tothe inlet of each 3-way valve 86. The controller 56 inputs a signalthrough line 116 causing selected 3-way valves 86 to accept the flow ofhot fluid from the distribution manifold 82 while closing the flow pathfrom valve(s) 86 into line 108. The hot fluid passes through the 3-wayvalve 86 into line 104 which connects to the inlet of pipe 68 of conduit66. At the same time, the controller 56 operates selected 3-way valves84 to open a flow path through such valve(s) 84 from the line 102connected to the pipe 70 of conduit 66 into line 106 extending betweenthe valve(s) 84 and hot fluid source 78. The inlet of 3-way valve 84connected to the distribution manifold 76 is closed. As a result, hotfluid from the source 78 and distribution manifold 82 passes through the3-way valve 86 into the pipe 68 of conduit 66 via line 104, and movesalong a channel 64 at the underside of top plate 60 thus locally heatingthe top plate 60 in that immediate area. The hot fluid enters the pipe70 of conduit 66 from the channel 64 and is transmitted to the line 102.After passing through the 3-way valve 84, the hot fluid is returned tothe source 78 through the line 106. The hot fluid is preferablycontinuously recirculated in the direction of arrows 120 in FIG. 5throughout the encapsulation process.

The support 22 of this invention therefore provides localized heatingand cooling of those areas of its top plate 60 where enhanced heat forencapsulation, or additional cooling to protect temperature sensitivecircuit elements 54, is desired. Depending upon how the valve pair 84,86 associated with each conduit 66 is operated, as described above,localized heating or cooling can be provided by each individual conduit66 or groups of conduits 66, as needed. This allows for the efficientencapsulation of LCP circuits 20 of essentially any configuration, oneafter the other. The flow of hot or cold fluid through any given conduit66 can be readily reversed by the controller 56, thus permitting thetemperature of the area of the top plate 60 immediately above to berapidly cooled if it was previously heated, or vice versa.

While the invention has been described with reference to a preferredembodiment, it should be understood by those skilled in the art thatvarious changes may be made and equivalents substituted for elementsthereof without departing from the scope of the invention. In addition,many modifications may be made to adapt a particular situation ormaterial to the teachings of the invention without departing from theessential scope thereof.

For example, the views in FIGS. 4 and 5 depict lines 106 and 108extending from the 3-way valves 84 and 86, respectively, directly to therespective fluid sources 78 and 72. It should be understood thatadditional distribution manifolds (not shown) could be provided betweenthese lines 106, 108 and the sources 72 and 78, if desired.

Therefore, it is intended that the invention not be limited to theparticular embodiment disclosed as the best mode contemplated forcarrying out this invention, but that the invention will include allembodiments falling within the scope of the appended claims.

1. Apparatus for sealing circuit elements of an electrical circuitbetween a substrate upon which the circuit elements are mounted and acover layer, at least some of the circuit elements on the substratebeing temperature sensitive, said apparatus comprising: a press having ahollow interior adapted to be connected to a source of heated fluid,said press having an exposed surface that is heated by the heated fluid;a support which carries the substrate and the cover sheet, said supportincluding: (i) a housing formed with a cavity and a plate having a firstsurface, said first surface of said plate supporting said substrate;(ii) a number of conduits mounted in said cavity, each of said conduitshaving a hollow interior that receives cooling fluid, said conduits eachbeing located relative to at least one discrete area along said firstsurface of said plate so as to be effective to cool said at least onediscrete area when cooling fluid is present within said hollow interiorthereof; (iii) said plate having a second surface formed with a numberof channels, said hollow interior of each of said conduits mounted insaid cavity of said housing of said support including a first flow pathand a second flow path communicating with one another through one ofsaid channels formed in said second surface of said plate, one of saidfirst and second flow paths forming an inlet adapted to receive coolingfluid from said source of cooling fluid and the other of said first andsecond flow paths forming an outlet adapted to return cooling fluid tosaid source of cooling fluid, the cooling fluid flowing though each ofsaid conduits contacting one of said channels in said second surface ofsaid plate and lowering the temperature of one of said discrete areas ofsaid support in the course of movement along said first and second flowpaths; a controller which is effective to direct cooling fluid into thehollow interior of individual ones of said conduits which are located atone or more discrete areas along said plate underlying the temperaturesensitive circuit elements carried on the substrate, said individualones of said conduits that receive cooling fluid providing localizedcooling of said top plate and the temperature sensitive circuit elementsat said discrete areas; said press, when at least partially filled withheating fluid, being movable relative to said support so that saidexposed surface of said press contacts the cover sheet which overliesthe substrate, said exposed surface of said press being effective toexert sufficient heat and pressure to cause the cover sheet andsubstrate to bond together while the heat sensitive circuit elementsoverlying said discrete areas of said top plate are cooled by saidindividual ones of said conduits receiving cooling fluid.
 2. Theapparatus of claim 1 in which said press is an iso-static press capableof exerting substantially equal pressure over the surface area of thecover sheet and substrate.
 3. The apparatus of claim 1 in which saidpress includes a flexible membrane engageable with the cover sheet, saidflexible membrane being formed of a material that substantially conformsto the shape of the circuit elements on the substrate in the course ofmovement into engagement with the cover sheet.
 4. The apparatus of claim1 further including thermal insulating compound located in between thetemperature sensitive circuit elements and the cover sheet.
 5. Theapparatus of claim 1 in which said conduit includes a first pipe havinga hollow interior defining said first flow path and a second pipe havinga hollow interior defining said second flow path, an upper end of eachof said first and second pipes being connected to one of said channelsin said second surface of said plate.
 6. The apparatus of claim 1 inwhich said conduits are adapted to connect to said source of heatedfluid, said controller being effective to direct heated fluid intoindividual ones of said conduits which are located at one or morediscrete areas along said plate that are spaced from the temperaturesensitive circuit elements on the substrate.
 7. The apparatus of claim 1in which each of the substrate and the cover layer are formed of liquidcrystal polymer.
 8. Apparatus for sealing circuit elements of anelectrical circuit between a substrate upon which the circuit elementsare mounted and a cover layer, at least some of the circuit elements onthe substrate being temperature sensitive, said apparatus comprising: apress having a hollow interior adapted to be connected to a source ofheated fluid, said press having an exposed surface that is heated by theheated fluid; a support which carries the substrate and the cover sheet,said support including: (i) a housing formed with a cavity and a topplate having a first surface, said first surface of said top platesupporting said substrate; (ii) a number of conduits mounted in saidcavity, each of said conduits having a hollow interior adapted to beconnected to a source of heating fluid and to a source of cooling fluid,each of said conduits being located relative to a discrete area alongsaid first surface of said plate so as to be effective to cool one ofsaid discrete area when cooling fluid is present within said hollowinterior thereof or to heat one of said discrete areas when heatingfluid is present within said hollow interior thereof; (iii) each of saidconduits mounted in said cavity including a first flow pathcommunicating with a second flow path, said cooling fluid passing thougheach of said conduits in one direction along said first and second flowpaths and said heating fluid passing through each of said conduits inthe opposite direction along said first and second flow paths; acontroller which is effective to direct cooling fluid into individualones of said conduits which are located at one or more of said discreteareas underlying the temperature sensitive circuit elements carried bysaid substrate on said first surface of said plate, said individual onesof said conduits that receive cooling fluid providing localized coolingof said plate at said one or more discrete areas underlying thetemperature sensitive circuit elements, said controller being effectiveto direct heating fluid into individual ones of said conduits which arelocated at one or more of said discrete areas that are spaced from thetemperature sensitive circuit elements carried by said substrate on saidfirst surface of said plate, said individual ones of said conduits thatreceive heating fluid providing localized heating of said top plate atsaid one or more discrete areas that are spaced from the temperaturesensitive circuit elements; said press, when at least partially filledwith heating fluid, being movable relative to said support so that saidexposed surface of said press contacts the cover sheet which overliesthe substrate, said press being effective to exert sufficient heat andpressure to cause the cover sheet and substrate to bond together whilethe heat sensitive circuit elements overlying said one or more discreteareas of said plate are cooled by said conduits receiving cooling fluidand one or more other discrete areas of said plate spaced from the heatsensitive elements are heated by said conduits receiving heating fluid.9. The apparatus of claim 8 in which said conduits which receive heatingfluid reach sufficient temperature to assist said press in causing thecover sheet and substrate to bond together.
 10. The apparatus of claim 8in which said press includes a flexible membrane engageable with thecover sheet, said flexible membrane substantially conforming to theshape of the circuit elements on the substrate in the course of movementinto engagement with the cover sheet.
 11. The apparatus of claim 8further including a layer of thermal insulating compound located inbetween the temperature sensitive circuit elements and the cover sheet.12. The apparatus of claim 8 in which each of said conduits mounted insaid cavity of said housing of said support includes a first flow pathcommunicating with a second flow path, one of said first and second flowpaths of each conduit forming an inlet adapted to receive cooling fluidfrom a source of cooling fluid and the other of said first and secondflow paths forming an outlet adapted to return cooling fluid to thesource of cooling fluid, one of said first and second flow paths of eachconduit forming an inlet adapted to receive heating fluid from a sourceof heating fluid and the other of said first and second flow pathsforming an outlet adapted to return heating fluid to the source ofheating fluid, said one of said first and second flow paths of eachconduit which forms an inlet for cooling fluid forms an outlet forheating fluid and said other one of said first and second flow paths ofeach conduit which forms an outlet for cooling fluid forms an inlet forheating fluid.
 13. The apparatus of claim 12 in which said conduitincludes a first pipe having a hollow interior defining said first flowpath and a second pipe having a hollow interior defining said secondflow path, said second surface of said top plate of said support beingformed with a channel connected to an upper end of each of said firstand second pipes, said channel interconnecting said hollow interiors ofsaid first and second pipes.
 14. The apparatus of claim 8 furtherincluding: a first pump located between a source of cooling fluid and afirst manifold; a first line connected between said first manifold andeach of said conduits, and a first 3-way valve mounted in each of saidfirst lines; a second pump located between a source of heating fluid anda second manifold; a second line connected between said second manifoldand each of said conduits, and a second 3-way valve mounted in each ofsaid second lines; a first return line connected between each of saidfirst 3-way valves and said source of heating fluid, and a second returnline connected between each of said second 3-way valves and said sourceof cooling fluid; said controller being operative to activate said firstpump and selected pairs of first and second 3-way valves to form a flowpath for cooling fluid from said source of cooling fluid, through saidfast manifold and first 3-way valve to said conduit, and then out ofsaid conduit, into said second line, through said second 3-way valve ofa valve pair and to said second return line connected to said source ofcooling fluid; said controller being operative to activate said secondpump and selected pairs of first and second 3-way valves to form a flowpath for heating fluid from said source of heating fluid through saidsecond manifold and second 3-way valve to said conduit, and then out ofsaid conduit, into said first line, through said first 3-way valve ofsaid valve pair and to said first return line connected to said sourceof heating fluid.
 15. The apparatus of claim 8 in which each of thesubstrate and the cover layer are formed of liquid crystal polymer. 16.Apparatus for sealing circuit elements of an electrical circuit betweena substrate upon which the circuit elements are mounted and a coverlayer, said apparatus comprising: a press having a hollow interior, saidpress being adapted to be connected to a source of heated fluid; asupport which carries the substrate and the cover sheet, at least someof the circuit elements on the substrate being temperature sensitive,said support including: (i) a housing formed with a cavity; (ii) anumber of conduits mounted in said cavity, each of said conduits havinga hollow interior adapted to be connected to the source of heated fluidand to a source of cooling fluid; (iii) each of said conduits includinga first flow path communicating with a second flow path, said coolingfluid passing through each of said conduits in one direction along saidfirst and second flow paths and said heating fluid passing through eachof said conduits in the opposite direction along said first and secondflow paths; a controller which is effective to direct cooling fluid fromthe source of cooling fluid into those of said conduits which arelocated in position underlying the temperature sensitive circuitelements on the substrate and to direct heating fluid from the source ofheating fluid into those of said conduits which are spaced from thetemperature sensitive circuit elements on the substrate; whereby saidpress when at least partially filled with heating fluid moves intocontact with the cover sheet overlying the substrate and exertssufficient heat and pressure to cause the cover sheet and substrate tobond together while the heat sensitive circuit elements are cooled bysaid conduits receiving cooling fluid.
 17. Apparatus for sealing circuitelements of an electrical circuit between a substrate upon which thecircuit elements are mounted and a cover layer, said apparatuscomprising: a press having a hollow interior, said press being adaptedto be connected to a source of heated fluid; a support which carries thesubstrate and the cover sheet, at least some of the circuit elements onthe substrate being temperature sensitive, said support including: (i) ahousing formed with a cavity; (ii) a number of conduits mounted in saidcavity, each of said conduits having a hollow interior adapted to beconnected to the source of heated fluid and to a source of coolingfluid; (iii) each of said conduits including a first flow pathcommunicating with a second flow path, one of said first and second flowpaths of each conduit forming an inlet adapted to receive cooling fluidfrom said source of cooling fluid and the other of said first and secondflow paths forming an outlet adapted to return cooling fluid to thesource of cooling fluid, one of said first and second flow paths of eachconduit forming an inlet adapted to receive heating fluid from saidsource of heating fluid and the other of said first and second flowpaths forming an outlet adapted to return heating fluid to the source ofheating fluid, said one of said first and second flow paths of eachconduit which forms an inlet for cooling fluid forms an outlet forhealing fluid and said other one of said first and second flow paths ofeach conduit which forms an outlet for cooling fluid forms an inlet forheating fluid; a controller which is effective to direct cooling fluidfrom the source of cooling fluid into those of said conduits which arelocated in position underlying the temperature sensitive circuitelements on the substrate, and to direct heating fluid from the sourceof heating fluid into those of said conduits which are spaced from thetemperature sensitive circuit elements on the substrate; whereby saidpress when at least partially filled with heating fluid moves intocontact with the cover sheet overlying the substrate and exertssufficient heat and pressure to cause the cover sheet and substrate tobond together while the heat sensitive circuit elements are cooled bysaid conduits receiving cooling fluid.
 18. The apparatus of claim 17 inwhich said conduit includes a first pipe having a hollow interiordefining said first flow path and a second pipe having a hollow interiordefining said second flow path, said support including a top plateformed with a channel connected to an upper end of each of said firstand second pipes, said channel interconnecting said hollow interiors ofsaid first and second pipes.
 19. Apparatus for sealing circuit elementsof an electrical circuit between a substrate upon which the circuitelements are mounted and a cover layer, said apparatus comprising: apress having a hollow interior, said press being adapted to be connectedto a source of heated fluid; a support which carries the substrate andthe cover sheet, at least some of the circuit elements on the substratebeing temperature sensitive, said support including: (i) a housingformed with a cavity; (ii) a number of conduits mounted in said cavity,each of said conduits having a hollow interior adapted to be connectedto the source of heated fluid and to a source of cooling fluid; a firstpump located between said source of cooling fluid and a first manifold;a first line connected between said first manifold and each of saidconduits, and a first 3-way valve mounted in each of said first lines; asecond pump located between said source of heating fluid and a secondmanifold; a second line connected between said second manifold and eachof said conduits, and a second 3-way valve mounted in each of saidsecond lines; a first return line connected between each of said first3-way valves and said source of heating fluid, and a second return lineconnected between each of said second 3-way valves and said source ofcooling fluid; a controller which is effective to activate said firstpump and selected pairs of first and second 3-way valves to form a flowpath for cooling fluid from said source of cooling fluid, through saidfirst manifold and first 3-way valve to those of said conduits which arelocated in position underlying the temperature sensitive circuitelements on the substrate, and then out of said conduits, into saidsecond line, through said second 3-way valve of a valve pair and to saidsecond return line connected to said source of cooling fluid; saidcontroller being effective to activate said second pump and selectedpairs of first and second 3-way valves to form a flow path for heatingfluid from said source of heating fluid through said second manifold andsecond 3-way valve to those of said conduits which are spaced from thetemperature sensitive circuit elements on the substrate, and then out ofsaid conduits, into said first line, though said first 3-way valve ofsaid valve pair and to said first return line connected to said sourceof heating fluid; whereby said press when at least partially filled withheating fluid moves into contact with the cover sheet overlying thesubstrate and exerts sufficient heat and pressure to cause the coversheet and substrate to bond together while the heat sensitive circuitelements are cooled by said conduits receiving cooling fluid.